Albert Barnes Commentary Deuteronomy 21:2

"then thy elders and thy judges shall come forth, and they shall measure unto the cities which are round about him that is slain:" — Deuteronomy 21:2 (ASV)

The elders represented the citizens at large, the judges the magistracy: priests (Deuteronomy 21:5) from the nearest priestly town were likewise to be at hand. Thus, all classes would be represented at the purging away of that blood-guiltiness which, until removed, attached to the whole community.